Fast acquisition of traffic channels for a highly variable data rate reverse link of a CDMA wireless communication system

ABSTRACT

A service option overlay for a CDMA wireless communication in which multiple allocatable subchannels are defined on a reverse link by assigning different code phases of a given long pseudonoise (PN) code to each subchannel. The instantaneous bandwidth needs of each on-line subscriber unit are then met by dynamically allocating none, one, or multiple subchannels on an as needed basis for each network layer connection. The system efficiently provides a relatively large number of virtual physical connections between the subscriber units and the base stations on the reverse link for extended idle periods such as when computers connected to the subscriber units are powered on, but not presently actively sending or receiving data. These maintenance subchannels permit the base station and the subscriber units to remain in phase and time synchronism. This in turn allows fast acquisition of additional subchannels as needed by allocating new code phase subchannels. Preferably, the code phases of the new channels are assigned according to a predetermined code phase relationship with respect to the code phase of the corresponding maintenance sub channel.

RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/088,413, filed Jun. 1, 1998, which is a continuation-in-part ofapplication Ser. No. 08/992,760, filed Dec. 17, 1997, and acontinuation-in-part of application Ser. No. 08/992,759, filed Dec. 17,1997, and a continuation-in-part of application Ser. No. 09/030,049,filed Feb. 24, 1998. The entire teachings of the above applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The increasing use of wireless telephones and personal computershas led to a corresponding demand for advanced telecommunicationservices that were once thought to only be meant for use in specializedapplications. In the 1980's, wireless voice communication became widelyavailable through the cellular telephone network. Such services were atfirst typically considered to be the exclusive province of thebusinessman because of expected high subscriber costs. The same was alsotrue for access to remotely distributed computer networks, whereby untilvery recently, only business people and large institutions could affordthe necessary computers and wireline access equipment. As a result ofthe widespread availability of both technologies, the general populationnow increasingly wishes to not only have access to networks such as theInternet and private intranets, but also to access such networks in awireless fashion as well. This is particularly of concern for the usersof portable computers, laptop computers, hand-held personal digitalassistants and the like who would prefer to access such networks withoutbeing tethered to a telephone line.

[0003] There still is no widely available satisfactory solution forproviding low cost, broad geographical coverage, high speed access tothe Internet, private intranets, and other networks using the existingwireless infrastructure. This situation is most likely an artifact ofseveral unfortunate circumstances. For one, the typical manner ofproviding high speed data service in the business environment over thewireline network is not readily adaptable to the voice grade serviceavailable in most homes or offices. Such standard high speed dataservices also do not lend themselves well to efficient transmission overstandard cellular wireless handsets. Furthermore, the existing cellularnetwork was originally designed only to deliver voice services. As aresult, the emphasis in present day digital wireless communicationschemes lies with voice, although certain schemes such as CDMA doprovide some measure of asymmetrical behavior for the accommodation ofdata transmission. For example, the data rate on an IS-95 forwardtraffic channel can be adjusted in increments from 1.2 kbps up to 9.6kbps for so-called Rate Set 1 and in for increments from 1.8 kbps up to14.4 kbps for Rate Set 2.

[0004] Existing systems therefore typically provide a radio channelwhich can accommodate maximum data rates only in the range of 14.4kilobits per second (kbps) at best in the forward direction. Such a lowdata rate channel does not lend itself directly to transmitting data atrates of 28.8 or even 56.6 kbps that are now commonly available usinginexpensive wireline modems, not to mention even higher rates such asthe 128 kbps which are available with Integrated Services DigitalNetwork (ISDN) type equipment. Data rates at these levels are rapidlybecoming the minimum acceptable rates for activities such as browsingweb pages. Other types of data networks using higher speed buildingblocks such as Digital Subscriber Line (xDSL) service are just nowcoming into use in the United States. However, their costs have onlybeen recently reduced to the point where they are attractive to theresidential customer.

[0005] Although such networks were known at the time that cellularsystems were originally deployed, for the most part, there is noprovision for providing higher speed ISDN- or xDSL-grade data servicesover cellular network topologies. Unfortunately, in wirelessenvironments, access to channels by multiple subscribers is expensiveand there is competition for them. Whether the multiple access isprovided by the traditional Frequency Division Multiple Access (FDMA)using analog modulation on a group of radio carriers, or by newerdigital modulation schemes the permit sharing of a radio carrier usingTime Division Multiple Access (TDMA) or Code Division Multiple Access(CDMA), the nature of the radio spectrum is that it is a medium that isexpected to be shared. This is quite dissimilar to the traditionalenvironment for data transmission, in which the wireline medium isrelatively inexpensive to obtain, and is therefore not typicallyintended to be shared.

[0006] Other considerations are the characteristics of the data itself.For example, consider that access to web pages in general isburst-oriented, with asymmetrical data rate transmission-requirements.In particular, the user of a remote client computer first specifies theaddress of a web page to a browser program. The browser program thensends this web page address data, which is typically 100 bytes or lessin length, over the network to a server computer. The server computerthen responds with the content of the requested web page, which mayinclude anywhere from 10 kilobytes to several megabytes of text, image,audio, or even video data. The user then may spend at least severalseconds or even several minutes reading the content of the page beforerequesting that another page be downloaded. Therefore, the requiredforward channel data rates, that is, from the base station to thesubscriber, are typically many times greater than the required reversechannel data rates.

[0007] In an office environment, the nature of most employees' computerwork habits is typically to check a few web pages and then to dosomething else for extended period of time, such as to access locallystored data or to even stop using the computer altogether. Therefore,even though such users may expect to remain connected to the Internet orprivate intranet continuously during an entire day, the actual overallnature of the need to support a required data transfer activity to andfrom a particular subscriber unit is actually quite sporadic.

SUMMARY OF THE INVENTION

[0008] Problem Statement

[0009] What is needed is an efficient scheme for supporting wirelessdata communication such as from portable computers to computer networkssuch as the Internet and private intranets using widely availableinfrastructure. Unfortunately, even the most modern wireless standardsin widespread use such as CDMA do not provide adequate structure forsupporting the most common activities, such as web page browsing. In theforward and reverse link direction, the maximum available channelbandwidth in an IS-95 type CDMA system is only 14.4 kbps. Due to IS-95being circuit-switched, there are only a maximum of 64 circuit-switchedusers that can be active at one time. In practicality, this limit isdifficult to attain, and 20 or 30 simultaneous users are typically used.

[0010] In addition, the existing CDMA system requires certain operationsbefore a channel can be used. Both access and traffic channels aremodulated by so-called long code pseudonoise (PN) sequences; therefore,in order for the receiver to work properly it must first be synchronizedwith the transmitter. The setting up and tearing down of channelstherefore requires overhead to perform such synchronization. Thisoverhead results in a noticeable delay to the user of the subscriberunit.

[0011] An attractive method of increasing data rate for a given user isthe sharing of channels in both the forward and reverse link direction.This is an attractive option, especially with the ease of obtainingmultiple access with CDMA; additional users can be supported by simplyadding additional codes for the forward link, or code phases in thereverse link for an IS-95 system. Ideally, this subchannel overheadwould be minimized so that when additional subchannels need to beallocated to a connection, they are available as rapidly as possible.

[0012] To maintain synchronization, it is therefore advantageous toprovide the sub-channels in such a way that the lowest possible speedconnection is provided on a reverse link while at the same timemaintaining efficient and fast ramp-up of additional code phase channelson demand. This in turn would maximize the number of availableconnections while minimizing the impact on the overall system capacity.

BRIEF DESCRIPTION OF THE INVENTION

[0013] The present invention is a service option overlay for anIS-95-like CDMA wireless communication system which accomplishes theabove requirements. In particular, a number of subchannels for a forwardlink are defined within a single CDMA radio channel bandwidth, such asby assigning different orthogonal codes to each sub-channel. Multiplesubchannels are defined on the reverse link by assigning different codephases of a given long pseudonoise (PN) code to each subchannel. Theinstantaneous bandwidth needs of each on-line subscriber unit are thenmet by dynamically allocating none, one, or multiple subchannels on anas needed basis for each network layer connection.

[0014] More particularly, the present invention efficiently provides arelatively large number of virtual physical connections between thesubscriber units and the base stations on the reverse link for extendedidle periods such as when computers connected to the subscriber unitsare powered on, but not presently actively sending or receiving data.These maintenance subchannels permit the base station and the subscriberunits to remain in phase and time synchronism. This in turn allows fastacquisition of additional subchannels as needed by allocating new codephase subchannels. Preferably, the code phases of the new channels areassigned according to a predetermined code phase relationship withrespect to the code phase of the corresponding maintenance subchannel.

[0015] In an idle mode, the subscriber unit sends a synchronization or“heartbeat” message on the maintenance subchannel at a data rate whichneed only be fast enough to allow the subscriber unit to maintainsynchronization with the base station. The duration of the heartbeatsignal is determined by considering the capture or locking range of thecode phase locking circuits in the receiver at the base station.

[0016] For example, the receiver typically has a PN code correlatorrunning at the code chip rate. One example of such a code correlatoruses a delay lock loop consisting of an early-late detector. A loopfilter controls the bandwidth of the loop which in turn determines howlong the code correlator must be allowed to operate before it canguarantee phase lock. This loop time constant determines the amount of“jitter” that can be tolerated; phase lock is typically considered to bemaintainable when this is equal to a fraction of a chip time, such asabout ⅛ of a chip time.

[0017] The heartbeat messages are preferably sent in time slots formedon the subchannels defined by the code phases. The use of time slottingallows a minimum number of dedicated base station receivers to maintainthe idle reverse links. In particular, the reverse maintenance channellinks are provided using multiple phases of the same long code as wellas by assigning a time slot on such code to each subscriber unit. Thisreduces the overhead of maintaining a large number of connections at thebase station.

[0018] Because of the time slotted nature of the reverse maintenancechannel, the base station receiver can also be time shared among thesevarious reverse links. To permit this, during each time slot allocatedto a particular subscriber unit, the base station receiver first loadsinformation concerning the last known state of its phase lock such asthe last known state of early-late correlators. It then trains theearly-late correlators for the required time to ensure that phase lockis still valid, and stores the state of the correlators at the end ofthe time slot.

[0019] When additional subchannels are required to meet bandwidthdemand, the additional code phases are assigned in a predetermined phaserelationship with respect to the locked code in order to minimizeoverhead transmissions which would otherwise be needed from the basestation traffic channel processor. As a result, many thousands of idlesubscriber units may be supported on a single CDMA reverse link radiochannel while at the same time minimizing start up delay when channelsmust be allocated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views.

[0021]FIG. 1 is a block diagram of a wireless communication systemmaking use of a bandwidth management scheme according to the invention.

[0022]FIG. 2 is a diagram showing how subchannels are assigned within agiven radio forward link frequency (RF) channel.

[0023]FIG. 3 is a diagram showing how subchannels are assigned within agiven reverse link RF channel.

[0024]FIG. 4 is a state diagram for a reverse link bandwidth managementfunction in the subscriber unit; and

[0025]FIG. 5 is a state diagram of the reverse link bandwidth managementfunction in the base station.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0026] Turning attention now to the drawings more particularly, FIG. 1is a block diagram of a system 100 for providing high speed data andvoice service over a wireless connection by seamlessly integrating adigital data protocol such as, for example, Integrated Services DigitalNetwork (ISDN) with a digitally modulated wireless service such as CodeDivision Multiple Access (CDMA).

[0027] The system 100 consists of two different types of components,including subscriber units 101-1, 101-2, . . . , 101-u (collectively,the subscriber units 101) and one or more base stations 170. Thesubscriber units 101 and base stations 170 cooperate to provide thefunctions necessary in order to provide wireless data services to aportable computing device 110 such as a laptop computer, portablecomputer, personal digital assistant (PDA) or the like. The base station170 also cooperates with the subscriber units 101 to permit the ultimatetransmission of data to and from the subscriber unit and the PublicSwitched Telephone Network (PSTN) 180.

[0028] More particularly, data and/or voice services are also providedby the subscriber unit 101 to the portable computer 110 as well as oneor more other devices such as telephones 112-1, 112-2 (collectivelyreferred to herein as telephones 112). The telephones 112 themselves mayin turn be connected to other modems and computers which are not shownin FIG. 1. In the usual parlance of ISDN, the portable computer 110 andtelephones 112 are referred to as terminal equipment (TE). Thesubscriber unit 101 provides the functions referred to as a networktermination type 1 (NT−1). The illustrated subscriber unit 101 is inparticular meant to operate with a so-called basic rate interface (BRI)type ISDN connection that provides two bearer or “B” channels and asingle data or “D” channel with the usual designation being 2B+D.

[0029] The subscriber unit 101 itself consists of an ISDN modem 120, adevice referred to herein as the protocol converter 130 that performsthe various functions according to the invention including spoofing 132and bandwidth management 134, a CDMA transceiver 140, and subscriberunit antenna 150. The various components of the subscriber unit 101 maybe realized in discrete devices or as an integrated unit. For example,an existing conventional ISDN modem 120 such as is readily availablefrom any number of manufacturers may be used together with existing CDMAtransceivers 140. In this case, the unique functions are providedentirely by the protocol converter 130 which may be sold as a separatedevice. Alternatively, the ISDN modem 120, protocol converter 130, andCDMA transceiver 140 may be integrated as a complete unit and sold as asingle subscriber unit device 101. Other types of interface connectionssuch as Ethernet or PCMCIA may be used to connect the computing deviceto the protocol converter 130. The device may also interface to anEthernet interface rather than an ISDN “U” interface.

[0030] The ISDN modem 120 converts data and voice signals between theterminal equipment 110 and 112 to format required by the standard ISDN“U” interface. The U interface is a reference point in ISDN systems thatdesignates a point of the connection between the network termination(NT) and the telephone company.

[0031] The protocol converter 130 performs spoofing 132 and basicbandwidth management 134 functions. In general, spoofing 132 consists ofinsuring that the subscriber unit 101 appears to the terminal equipment110, 112 that is connected to the public switched telephone network 180on the other side of the base station 170 at all times. The bandwidthmanagement function 134 is responsible for allocating and deallocatingCDMA radio channels 160 as required. Bandwidth management 134 alsoincludes the dynamic management of the bandwidth allocated to a givensession by dynamically assigning sub-portions of the CDMA radio channels160 in a manner which is more fully described below.

[0032] The CDMA transceiver 140 accepts the data from the protocolconverter 130 and reformats this data in appropriate form fortransmission through a subscriber unit antenna 150 over CDMA radio link1160-1. The CDMA transceiver 140 may operate over only a single 1.25 MHzradio frequency channel or, alternatively, in a preferred embodiment,may be tunable over multiple allocatable radio frequency channels.

[0033] CDMA signal transmissions are then received and processed by thebase station equipment 170. The base station equipment 170 typicallyconsists of multichannel antennas 171, multiple CDMA transceivers 172,and a bandwidth management functionality 174. Bandwidth management 174controls the allocation of CDMA radio channels 160 and subchannels, in amanner analogous to the subscriber unit 101. The base station 170 thencouples the demodulated radio signals to the Public Switch TelephoneNetwork (PSTN) 180 in a manner which is well known in the art. Forexample, the base station 170 may communicate with the PSTN 180 over anynumber of different efficient communication protocols such as primaryrate ISDN, or other LAPD based protocols such as IS-634 or V5.2.

[0034] It should also be understood that data signals travelbidirectionally across the CDMA radio channels 160. In other words, datasignals received from the PSTN 180 are coupled to the portable computer110 in a forward link direction, and data signals originating at theportable computer 110 are coupled to the PSTN 180 in a so-called reverselink direction. The present invention involves in particular the mannerof implementing the reverse link channels.

[0035] Continuing to refer to FIG. 1 briefly, spoofing 134 thereforeinvolves having the CDMA transceiver 140 loop back these synchronousdata bits over the ISDN communication path to spoof the terminalequipment 110, 112 into believing that a sufficiently wide wirelesscommunication link 160 is continuously available. However, only whenthere is actually data present from the terminal equipment to thewireless transceiver 140 is wireless bandwidth allocated. Therefore, thenetwork layer need not allocate the assigned wireless bandwidth for theentirety of the communications session. That is, when data is not beingpresented upon the terminal equipment to the network equipment, thebandwidth management function 134 deallocates initially assigned radiochannel bandwidth 160 and makes it available for another transceiver andanother subscriber unit 101.

[0036] In order to better understand how bandwidth management 134 and174 accomplish the dynamic allocation of radio channels, turn attentionnow to FIG. 2. This figure illustrates one possible frequency plan forthe wireless links 160 according to the invention. In particular, atypical transceiver 170 can be tuned on command to any 1.25 MHz channelwithin a much larger bandwidth, such as up to 30 MHz. In the case oflocation in an existing cellular radio frequency bands, these bandwidthsare typically made available in the range of from 800 to 900 MHz. Forpersonal communication systems (PCS) type wireless systems, thebandwidth is typically allocated in the range from about 1.8 to 2.0GigaHertz (GHz). In addition, there are typically two matching bandsactive simultaneously, separated by a guard band, such as 80 MHz; thetwo matching bands form forward and reverse full duplex link.

[0037] Each of the CDMA transceivers, such as transceiver 140 in thesubscriber unit 101, and transceivers 172 in the base station 170, arecapable of being tuned at any given point in time to a given 1.25 MHzradio frequency channel. It is generally understood that such 1.25 MHzradio frequency carrier provides, at best, a total equivalent of about500 to 600 kbps maximum data rate transmission within acceptable biterror rate limitations.

[0038] In contrast to this, the present invention subdivides theavailable approximately 500 to 600 kbps data rate into a relativelylarge number of subchannels. In the illustrated example, the bandwidthis divided into sixty-four (64) subchannels 300, each providing an 8kbps data rate. A given subchannel 300 is physically implemented byencoding a transmission with one of a number of different assignablepseudorandom codes. For example, the 64 subchannels 300 may be definedwithin a single CDMA RF carrier by using a different orthogonal code foreach defined subchannel 300 for example, for the forward link.

[0039] As mentioned above, subchannels 300 are allocated only as needed.For example, multiple subchannels 300 are granted during times when aparticular ISDN subscriber unit 101 is requesting that large amounts ofdata be transferred. These subchannels 300 are quickly released duringtimes when the subscriber unit 101 is relatively lightly loaded.

[0040] The present invention relates in particular to maintaining thereverse link so that synchronization of the subchannels does not need tobe reestablished each time that channels are taken away and then grantedback.

[0041]FIG. 3 is a diagram illustrating the arrangement of how thesubchannels are assigned on the reverse link. It is desirable to use asingle radio carrier signal on the reverse link to the extent possibleto conserve power as well as to conserve the receiver resources whichmust be made available at the base station. Therefore, a single 1.2288MHz band 350 is selected out of the available radio spectrum.

[0042] A relatively large number, N, such as 1000 individual subscriberunits are then supported by using a single long pseudonoise (PN) code ina particular way. First, a number, p, of code phases are selected fromthe available 2⁴²−1 different long code phases. A given long code phaseis unique to a particular subscriber unit and never changes. As will beexplained, this is also true for supplemental code phases as well. Thecode p phases shifts are then used to provide p subchannels. Next, eachof the p subchannels are further divided into s time slots. The timeslotting is used only during the idle mode, and provides two advantages;it reduces the numbers of “maintenance” receivers in the base station,and it reduces the impact to reverse channel capacity by reducingtransmit power and thus interference. Therefore, the maximum supportablenumber of supportable subscriber units, N, is p times s. During Idlemode, use of the same PN code with different phases and time slotsprovides many different subchannels with permits using a single rakereceiver in the base station 104.

[0043] In the above mentioned channel allocation scheme, radio resourcesare expected to be allocated on an as-needed basis. However,consideration must also be given to the fact that normally, in order setup a new CDMA channel, a given reverse link channel must be given timeto acquire code phase lock at the receiver. The present invention avoidsthe need to wait for each channel to acquire code phase lock each timethat it is set up by several mechanisms which are describe more fullybelow. In general, the technique is to send a maintenance signal at arate which is sufficient to maintain code phase lock for each subchanneleven in the absence of data.

[0044] The objective here is to minimize the size of each time slot,which in turn maximizes the number of subscribers that can be maintainedin an idle mode. The size, t, of each time slot is determined by theminimum time that it takes to guarantee phase lock between thetransmitter at the subscriber unit and the receiver in the base station.In particular, a code correlator in the receiver must receive amaintenance or “heartbeat” signal consisting of at least a certainnumber of maintenance bits over a certain unit of time. In the limit,this heartbeat signal is sent by sending at least one bit from eachsubscriber unit on each reverse link at a predetermined time, e.g., itsdesignated time slot on a predetermined one of the N subchannels.

[0045] The minimum time slot duration, t, therefore depends upon anumber of factors including the signal to noise ratio and the expectedmaximum velocity of the subscriber unit within the cell. With respect tosignal to noise ratio, this depends on

Eb/No+Io

[0046] where Eb is the energy per bit, No is the ambient noise floor,and Io is the mutual interference from other coded transmissions of theother sub-channels on the reverse link sharing the same spectrum.Typically, to close the link requires integration over 8 chip times atthe receiver, and a multiple of 20 times that is typically needed toguarantee detection. Therefore, about 160 chip times are typicallyrequired to correctly receive the coded signal on the reverse link. Fora 1.2288 MHz code, Tc, the chip time, is 813.33 ns, so that this minimumintegration time is about 130 μs. This in turn sets the absolute minimumduration of a data bit, and therefore, the minimum duration of a slottime, t. The minimum slot time of 130 μs means that at a maximum, 7692time slots can be made available per second for each phase coded signal.

[0047] To be consistent with certain power control group timingrequirements, the time slot duration can be relaxed somewhat. Forexample, in the IS-95 standard, a power control group timing requirementrequires a power output sample from each subscriber unit every 1.25 ms.

[0048] Once code phase lock is acquired, the duration of the heartbeatsignal is determined by considering the capture or locking range of thecode phase locking circuits in the receiver at the base station. Forexample, the receiver typically has a PN code correlator running at thecode chip rate. One example of such a code correlator uses a delay lockloop consisting of an early-late detector. A loop filter controls thebandwidth of this loop which in turn determines how long the codecorrelator must be allowed to operate before it can guarantee phaselock. This loop time constant determines the amount of “jitter” that canbe tolerated in the code correlator, such as about ⅛ of a chip time, Tc.

[0049] In the preferred embodiment, the system 100 is intended tosupport so-called nomadic mobility. That is, high mobility operationwithin moving vehicles typical of cellular telephony is not expected tobe necessary. Rather, the typical user of a portable computer who isactive is moving at only brisk walking speeds of about 4.5 miles perhour (MPH). At 4.5 MPH, corresponding to a velocity of 6.6 feet persecond, a user will move 101 feet in ⅛ of the 1/1.2288 MHz chip time(Tc). Therefore, it will take about 101 feet divided by 6.6 feet, orabout 15 seconds for such a user to move distance which is sufficientlyfar for him to a point where the code phase synchronization loop cannotbe guaranteed to remain locked. Therefore, as long as a completesynchronization signal is sent for a given reverse link channel every 15seconds, the reverse link loop will therefore remain in lock.

[0050]FIG. 4 is a state diagram for a reverse link bandwidth managementfunction in the subscriber unit. In an idle mode 400, a first state 401is entered in which the subscriber unit receives a time slot assignmentfor its code phase reverse channel. This time slot is only used in theidle mode. The same long code phase is pre-assigned and is permanent tothe subscriber unit.

[0051] In a next state 402, the heartbeat signal is sent in the assignedtime slots. A state 403 is then entered in which the subscriber unitmonitors its internal data buffers to determine whether additional codephase channels are required to support the establishment of a reverselink with sufficient bandwidth to support and active traffic channel. Ifthis is not the case, then the subscriber returns to state 402 andremains in the idle mode 400.

[0052] Prior to entering the Active state 4050 from Idle mode 400, thesubscriber unit must make a request to the base station. If granted,(step 403-b), processing proceeds to step 451, and if not granted,processing proceeds to step 402. However, the subscriber unit knows thatit is assigned code phase channels in a predetermined relationship tothe code phase channel of its fundamental channel, i.e.,

P _(n+1)

=

{P _(o)}

[0053] where P_(n+1) is the code phase for the new channel (n+1), andP_(o) is the code phase assigned to the fundamental channel for theparticular subscriber. Such a code phase relationship

may be, for example, to select uniformly from the available 24² codes,every 24²/2¹⁰'th or every 2³²'th code phase in a system which issupporting 1024 (2¹⁰) reverse links, for a single subscriber.

[0054] A number, C, of these new code phases are thereforeinstantaneously calculated based simply upon the number of additionalcode phase channels, and without the need to require code phasesynchronization for each new channel.

[0055] After step 452 is processed, a request is made for code phasechannels. If granted (step 452-b), processing proceeds to step 453, andif not granted, processing proceeds to step 451 in order to process theadditional channel requests. In a next state 453, the subscriber unitbegins transmitting its data on its assigned code phase channels. Instate 454, it continues to monitor its internal data buffers and itsassociated forward access channel to determine when to return to theidle mode 400, to to state 451, to determine if new code phase channelsmust be assigned, or to state 455, where they are deallocated.

[0056]FIG. 5 is a state diagram of idle mode processing in the reverselink management function in the base station 104. In a first state 501,for each idle subscriber unit 101, a state 502 is entered in which astored state of the correlators for the present time slot (p,s) from aprevious synchronization session is read. In a next state 503, anearly-late correlator is retrained for the time slot duration, t. In anext state 504, the correlator state is stored; in state 505, the loopis continued for each subscriber.

[0057] Equivalents

[0058] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

[0059] For example, instead of ISDN, other wireline and networkprotocols may be encapsulated, such as xDSL, Ethernet, and X.25, andtherefore may advantageously use the dynamic wireless subchannelassignment scheme described herein.

[0060] Those skilled in the art will recognize or be able to ascertainusing no more than routine experimentation, many equivalents to thespecific embodiments of the invention described specifically herein.Such equivalents are intended to be encompassed in the scope of theclaims.

[0061] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method for providing wireless communication ofdigital signals, the digital signals being communicated between aplurality of wireless subscriber units and a base station, the digitalsignals being communicated using at least one radio frequency channelvia Code Division Multiple Access (CDMA) modulated radio signals, thedigital signals also having a given nominal data rate, the methodcomprising the steps of: a) making available a plurality of subchannelswithin each CDMA radio channel, wherein a data rate of each subchannelis much less than the nominal data rate of the digital signals; b)allocating available subchannels only on an as-needed basis, wherein thenumber of subchannels allocated is variable during the duration of agiven session; and c) on a reverse link, providing an idling modeconnection for subscriber units which are powered on, but not presentlyactively sending data, wherein the idling mode connection is operable toenable to subchannels to be reallocated without reestablishing a bitsynchronization with the base station.
 2. A method as in claim 1 whereinthe step of providing an idling mode connection the subscriber unitsends a heartbeat signal at a data rate which is low enough to maintainthe bit synchronization with the base station.
 3. A method as in claim 2wherein the data rate of the heartbeat signal is from about 37 to 80bps.
 4. A method as in claim 1 wherein in order to reduce the overheadof maintaining the connections, instead of assigning a different Walshcode to each subscriber, the subscriber units use the same PN long codebut at different code phases.
 5. A method as in claim 2 wherein theheartbeat message is time slotted between inactive links, to allow fewerdedicated base station receivers to maintain the links.
 6. A method asin claim 1 wherein to enter an active state, the subscriber unit sends acommand requesting a higher data service rate.
 7. A method as in claim 6wherein upon receiving a request for higher capacity data or voicetraffic, the base station hands the link to a reverse channel trafficprocessor, and the higher rate is then made available by the basestation assigning additional code phases to the subscriber unit.
 8. Amethod as in claim 7 wherein the additional code phases are assigned ina predetermined phase relationship to minimize overhead transmissionsfrom the base station traffic channel processor.
 9. A method as in claim6 wherein the ramp-up of data rate may occur in two phases, with thesubscriber unit first being granted only access to a lower availablerate channel, prior to granting access to a full rate channel.
 10. Amethod as in claim 1 wherein if the base station determines that themaximum data rate for one connection is not enough, additional codechannels are assigned to the subscriber.
 11. A method as in claim 10wherein the additional channels have a predetermined relationship to theoriginal code phase.
 12. A method as in claim 1 wherein a plurality ofsubchannels are made available on a single radio frequency carrier byassigning orthogonal codes for each subchannel.